In an LTE (Long Term Evolution)-Advanced scheme, it is possible to use a relay node RN connectable through a Un interface, for a radio base station DeNB (Donor eNB).
It is defined that in an attach process of the relay node RN, the relay node RN performs an attach process (Phase-1) similar to that executed by a mobile station UE and then performs an attach process (Phase-2) executed as the relay node RN (Non Patent Literatures 1 and 2).
Hereinafter, with reference to FIG. 4, the attach process executed as the relay node RN will be simply described.
As illustrated in FIG. 4, in step S2001, when “USIM-RN (Universal Subscriber Identity Module-RN, a subscriber identification module for a relay node)” is not active, the relay node RN sets the USIM-RN to active and restores (or reconfigures) a secure channel between the relay node RN and the USIM-RN.
In addition, the USIM-RN can be accessed only through the secure channel.
In such a case, the relay node RN invalidates “EPS security context” in the USIM-RN.
In step S2002, the relay node RN transmits, to a radio base station DeNB, “Attach Request (RN) (an attach request signal)” for requesting an attach process executed as the relay node RN.
Furthermore, the relay node RN transmits “Attach Request” including IMSI (International Mobile Subscriber Identity) or GUTI (Global Unique Temporary Identifier) related to the USIM-RN.
In step S2003, the radio base station DeNB transmits “(S1) Initial UE message (an initial signal)” to a mobile management node MME (Mobility Management Entity).
In response to the “(S1) Initial UE message”, the mobile management node MME performs “EPS-AKA (Evolved Packet System-Authentication and Key Agreement, an authentication and key agreement procedure)” between the relay node RN and the USIM-RN in step S2004, and sets NAS (Non Access Stratum) security between the mobile management node MME and the relay node RN in step S2005.
Furthermore, the relay node RN uses only a key received from the USIM-RN through the secure channel.
In step S2006, the mobile management node MME determines whether the USIM-RN can be used for the attach process executed as the relay node RN on the basis of subscriber data (subscription data) acquired from a subscriber management server HSS (Home Subscriber Server.)
In step S2007, the mobile management node MME transmits “(S1) Initial Context Setup Request” including a result of the determination to the radio base station DeNB.
When the result of the determination indicates that the USIM-RN can be used for the attach process executed as the relay node RN, the radio base station DeNB sets AS (Access Stratum) security in step S2009 and sets AS security for the relay node RN for S1/X2 DRB (Data Radio Bearer) in step S2010.
When the result of the determination indicates that the USIM-RN cannot be used for the attach process executed as the relay node RN, the radio base station DeNB rejects the attach process of the relay node RN.